Archive for the ‘astronomy’ Category

“Deep” sky with Nikon D90

Tuesday, February 17th, 2009

The Nikon D90 has a very low “dark current”, which makes it better suitable than the previous D70 and D80 for “deep” sky photo’s. Here are some examples:

Core of the the Orion nebula:

4x 30s ISO1600 @F10(?) C8/LXD75 mount, rough polar alignment

orion-stack-small.jpg

Pleiades: (f=200mm f/5.6 ISO200, 4x 180s)

pleiades.jpg

Orion as a whole:

zoek-orion.jpg

Andromeda nebula:

average-of-dsc_0182to0184-pixinsight.jpg

Simplified Bahtinov focussing mask

Tuesday, February 17th, 2009

A Bahtinov mask is a mask on a telescope that produces a line pattern that shows whether you are focussed well, and even shows if you are front or back focussed if not properly focussed. It requires a quite complicated mask, but almost the same effect can be achieved with 2 wires stuck to the aperture:

dsc_0672_resize.jpg

This results in a line pattern (Bahtinov results in dotted lines of 1st, 2nd etc order diffraction patterns):

montage.jpg

But it still tells you where your current focus is (front, back or in focus):

poormans_bahtinov.gif

New “de-striped” Virtual Moon Atlas available

Friday, May 23rd, 2008

Release 4 of the Virtual Moon Atlas is now available with destriped LOPAM image database:

vma4.jpg

Live image stacking

Sunday, February 10th, 2008

Just like Registax, but live this time. How does it work?

- acquire images via webcam (I use the Philips Toucam 840k, 640×480 mode).

- center images based on the “center of mass” of the image or register the new image via “phase correlation” to the first in stack

In case of center of mass: set the threshold slider above noise level and the image will be centered on its center of mass. This works for a planet or star image, not for images showing only part of the moon.

- a stack of 16 images is kept, but larger and smaller stacks can be selected

- the sharpness of each incoming image is measured (variance/mean brightness)

- if the “sharpness” exceeds that of any of the images in the stack, the least sharp image is replaced with the new image

- the “live” tab shows the incoming frames, the “stacked” tab shows the average of the images in the stack

As more time passes, hopefully sharper and sharper images will be acquired, resulting in a sharper stacked image.

release.zip

This software was made on .NET, so you will need the .NET framework as well if not already installed.

Screenshots:

live.jpg

stacked.jpg

Comet 17P/Holmes

Saturday, November 3rd, 2007

An unexpectedly bright comet, already heading away from the sun close to Mel20 in Perseus:

piggyback on the C8/LXD75

comet-17p-holmes.jpg

And a bit closer: C8, f/5.6 focal reducer and 2x barlow allowed for prime focus photography (bit awkward, maybe should heve left all the extra glass out but there was little time to try between the clouds passing over head). The comet fully filled the 10 megapixel frame

dsc_2072-crop-downsize-median4.JPG

Heliochronometer

Friday, September 14th, 2007

Intrigued by wanting to tell time accurately by looking at sun’s position, I built the following after browsing the internet.

If you know all exceptone of these, you can tell the value of the missing one:

- Longitude

-Latitude

- time (Summer or Winter)

- north-south direction

- date

- levelness (spirit level)

Normally you would use it to tell time of course. Brass versions of this apparatus were used to tell time accurately until radio was invented to transmit an accurate time signal to the rest of the world.

dsc_1828_resize.JPG

dsc_1825_resize.JPG

dsc_1829_resize.JPG

dsc_1826_resize.JPG

Framelet lines be gone

Saturday, September 8th, 2007

A lot of great moon imagery is available from old missions on film. Put together these films give very high resolution “panoramas”. Unfortunately a lot of lines are visible between the films and even within the film.

I wrote a short algorithm in Matlab to remove the lines 90% (see below).

UPDATES:

- this post grew into an “Lunar Picture of the Day” on September 13th 2007. This includes the Matlab Code and a short explanation.

- the new release of Virtual Atlas of the Moon will contain more than 1.000 orbiter images that were cleaned using this algorithm

- here are 2 samples in 20 MegaPixel: Plato and the Alpine Valley .
- and a 50 Mpixel pano of the two:
Plato+Alpes pano

- a stand alone executable is now available:

1. download and run the matlab component library
2. download the actual routine itself, and rename the .ex_ files to .exe, and you should be ready destripe yourself.

Snapshot of the application:

horlinremove.jpg

linesnolines1.gif

linesnolines2.gif

Andromeda nebula (M31, but also M110 and M32)

Saturday, August 11th, 2007

Visible with the naked eye, even in summer. The image shows stars roughly to magnitude 13/14.

In the lower left the weak (magnitude 9) NGC185 and NGC147 can be seen.

7 exposures of 30s stacked, ISO800 with a 85mm f/1.8 lense. Full 10 MP.

andromeda_subtract.jpg

Uranus

Saturday, August 11th, 2007

First time I managed to find and image Uranus.

August 10th, 23h28 UT, 3.7 arc seconds small (= like inspecting a human iris from 1000 m away)  and 26 deg above the horizon with a remarkably good seeing.

uranus.jpg

We have got him: GRS

Tuesday, July 17th, 2007

After all the calculations it occurred to me that I checked the clock just when a GRS transit was occurring. After the clouds presented a hole to image through I got this: quite nice considering the horrible seeing.

July 17th 2007, 21h28 UTC. The transit was predicted 21h01 so GRS must have moved 16 degrees past the central meridian assuming it is at 119 degrees longitude. The tangent of 16 degrees=16/60=0.25 so the GRS must have moved about 0.25 times the radius of Jupiter, which seems to agree more or less with the image.
In addition a Europa and its shadow are visible!

2007_07_17_21h28-ut-jup1-rgb-alignwavelet-levels2.jpg

A simulation/prediction of the GRS position at 21h28:

jup-map-2007_07_17_21h28.jpg